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Just how the unusual and complex sounds of the didjeridu - an ancient traditional instrument of the people of Arnhem Land - are created is not well understood, but that could change with a new Australian project.

A research collaboration between physicists, and medical imaging specialists will be working on the project for the next three years with an Australian Research Council Discovery Grant to study the acoustics of the didjeridu.

"People look at it and say it's very primitive," said Associate Professor Lloyd Hollenberg, a theoretical physicist at the University of Melbourne. "They don't even take it seriously as a musical instrument, but when you look at it it's very complicated, and not easy to play."

"The pipe, to a large extent is the least important part of the didjeridu," he added. "The didjeridu really is inside the body."

The unique sound of the didjeridu comes from the complex interaction between the pipe (or "tube") with the mouth and vocal tract of the player. The way the lips couple with the pipe, the movements made within the vocal tract, and the control of breathing all have a profound effect on the sound. The researchers are looking at these individual components to see how they work together.

Tricks of the trade

The droning noise comes from the pipe. "But all of the complicated things a didjeridu player does - such as the call of a kookaburra - are achieved by controlling the shape of the vocal tract," explained Dr Hollenberg. "You are singing down the instrument basically."

It's the movement of the tongue that determines the shape of the vocal tract but until now no one has known precisely how that happens. The solution has been to use Magnetic Resonance Imaging (MRI). Dr Hollenberg constructed a special didjeridu so he could lie perfectly still inside the MRI machine and play notes. "In the end I did it myself," he said, "one of the many horrific experiments I have conducted on myself in the course of science."

In the celebrated technique of circular breathing, some of the air inhaled through the nose is stored inside your cheeks. You can use this air to blow through the instrument while catching your next breath - not dissimilar to bagpipes. "When you play the didjeridu you don't need a lot of air - you can keep a note up without even breathing for about 30 seconds, its gentle exhalation," Hollenberg explained.

Didjeridu beginnings

The didjeridu originated in the northern area of Australia. The traditional guardians are considered to be the Yolngu people in Arnhem Land. They call the instrument a yidaki.

Usually a didjeridu is made from a lopped eucalyptus sapling that has had a termite nest at its base. The white ants will have eaten out the centre of the tree, leaving behind a spongy material that the instrument maker can easily push out.

"Then they thin the edges - the real art form to making a good didjeridu," explained Dr Hollenberg. The thinning of the walls affects the timbre of the sound. The length of the instrument determines the primary pitch of the note. All of the higher pitched sounds present in didjeridu playing originate from the acoustics of the vocal tract.

While the didjeridu is now played all over Australia, this only happened after white settlement in the country. Those that are made in the south are often made from mallee wood and produce a very different sound, according to Dr Hollenberg.

Dr Hollenberg began playing the didjeridu in 1994. As a physicist, he became curious as to how the sounds are made. He could only find two papers on the didjeridu. The first, dated 1983, was written by Professor Neville Fletcher from Australian National University. "He's the real pioneer," enthused Dr Hollenberg. "Its terrific he's on board."

The other members of the team are Associate Professor Joe Wolfe and Dr John Smith from the University of NSW. They are all physicists, and with the exception of Dr Hollenberg are specialists in acoustics. As a theoretical physicist, he has had to teach himself acoustics.

"We are looking at this as non-indigenous Australians doing a scientific investigation which is not the way indigenous people would look at it," said Dr Hollenberg. "So we try to have a balance there by liaising with indigenous players."